We obtain a blue phosphor, Ba9Lu2Si6O24:Eu2+ (BLS:Eu2+), which shows a strong emission peak at 460 nm and a weak tail from 460 to 750 nm. A 610 nm red emission is observed for the first time in this kind of rhombohedral structure material, which is much different from the same crystal structure of Ba9Sc2Si6O24:Eu2+ and Ba9Y2Si6O24:Eu2+. The luminescence properties and decays from 10 to 550 K are discussed. The new red emission arises from a trapped exciton state of Eu2+ at the Ba site with a larger coordination number (12-fold). It exhibits abnormal luminescence properties with a broad bandwidth and a large Stokes shift. Under the 400 nm excitation, the external quantum efficiency of BLS:Eu2+ is 45.4%, which is higher than the 35.7% for the commercial blue phosphor BAM:Eu2+. If the thermal stability of BLS:Eu2+ can be improved, it will show promising applications in efficient near-UV-based white LEDs.